Advance GTA

Unlock All tracks
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Hold L + R, then press Up/Right + B at the Start screen.
Unlock All cars
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Hold L + R, then press Up/Left + B at the Start screen.
Get All tune-ups
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Hold L + R, then press Down/Right + B at the Start screen.
Mini cars
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Hold L + R, then press Right + B at the Start screen.
F1 car
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Hold L + R, then press Left + B at the Start screen.
View credits
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Hold L + R, then press Up + B at the Start screen.
Formula 1 Mode:
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To access the Extra Formula 1 mode play through the championship
mode and beat all four of the classes with a first place in each
race. You will get a new car after the last race. It is a Formula
1 race car. At the menu screen the Extra 2 option will be available.
Hidden Go-Kart Mode:
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To access the Extra Go-Kart mode play through the championship mode
and beat the beginners, middle, and high-speed classes. You should
get a new car after the last race you win that is a go-kart and then
go to the main menu and the first option that was unlockable will
say extra.